Oximeter sensor temperature control

Abstract

A system for measuring blood oxygen saturation uses a noninvasive optical technique. A patient's arterial blood is illuminated with light at two different wavelengths and the intensity of the reflected light is correlated with an oxygen saturation reference curve to determine the oxygen saturation of the patient's blood. The optical sensor includes one or more controlled heat sources which are used to maintain the patient's tissue at a predetermined temperature. Safety circuits are also provided in order to prevent thermal burns to a patient in the event of a system failure.

What is claimed is: 
     
       1. A blood oxygen saturation monitoring system for non-invasive measurement of oxygen saturation of arterial blood in tissue of a patient, comprising: a first source of electromagnetic radiation at a first wavelength;   a second source of electromagnetic radiation at a second wavelength;   means for positioning said first and second sources of electromagnetic radiation on the patient so as to illuminate a sample of blood in the tissue;   detecting means for receiving electromagnetic radiation reflected by said sample of blood;   data processing means for calculating the blood oxygen saturation of said tissue responsive to said detected reflected electromagnetic radiation; and   means for maintaining said tissue at a predetermined temperature responsive to the temperature of said tissue.   
     
     
       2. The blood oxygen saturation monitoring system according to claim 1, wherein said means for maintaining said tissue at a predetermined temperature comprises a light emitting diode. 
     
     
       3. The blood oxygen monitoring system according to claim 2, wherein said means for maintaining said tissue at a predetermined temperature further comprises a thermal sensor in the form of a thermal sensor, said thermistor providing an output signal indicative of the temperature of said tissue. 
     
     
       4. The blood oxygen monitoring system according to claim 3, wherein said means for maintaining said tissue at a predetermined temperature further comprises a control circuit responsive to said output signal of said thermal sensor, said control circuit comprising a feedback circuit with an adjustable setpoint. 
     
     
       5. The blood oxygen monitoring system according to claim 4, wherein said control circuit further comprises a core temperature probe for monitoring a patient's body temperature to provide a reference signal which indicates the desired setpoint. 
     
     
       6. The blood oxygen monitoring system according to claim 3, further comprising safety means coupled to said means for maintaining for disabling said means for maintaining to thereby; prevent thermal burns to said tissue in the event of a system failure. 
     
     
       7. The blood oxygen monitoring system according to claim 6, wherein said safety means comprises a thermal sensor failure circuit for detecting a failure in the thermal sensor, and means for disabling said light emitting diode when a failure is detected by said thermal sensor failure circuit. 
     
     
       8. The blood oxygen monitoring system according to claim 6, wherein said safety means comprises a power sensing circuit for monitoring the power delivered to said light emitting diode, and means for disabling said light emitting diode if the delivered power exceeds a predetermined value. 
     
     
       9. The blood oxygen monitoring system according to claim 8, wherein said power sensing circuit monitors the average delivered power. 
     
     
       10. The blood oxygen saturation monitoring system of claim 3, wherein said thermal sensor comprises a thermistor. 
     
     
       11. The blood oxygen monitoring system according to claim 1, further comprising safety means coupled to said means for maintaining for disabling said means for maintaining thereby preventing thermal burns to said tissue in the event of a system failure. 
     
     
       12. The blood oxygen saturation monitoring system of claim 1, wherein said predetermined temperature is about 37° C. 
     
     
       13. A blood oxygen saturation monitoring system for noninvasive measuring of arterial blood oxygen saturation in tissue of a patient comprising: a first source of electromagnetic radiation at a first wavelength;   a second source of electromagnetic radiation at a second wavelength;   means for positioning said first and second sources of electromagnetic radiation on the patient so as to illuminate a sample of blood in tissue;   detecting means for receiving electromagnetic radiation reflected by said sample of blood;   data processing means for computing the blood oxygen saturation of said tissue responsive to said detected reflected electromagnetic radiation;   a light emitting diode producing electromagnetic radiation for heating said tissue;   means for controlling said light emitting diode thereby maintaining said tissue at a predetermined temperature; and   safety means for disabling said light emitting diode thereby preventing thermal burns to said tissue in the event of a system failure.   
     
     
       14. The blood oxygen saturation monitoring system of claim 13, wherein said predetermined temperature is about 37° C. 
     
     
       15. A method for determining the oxygen saturation of arterial blood in tissue, comprising the steps of: illuminating a sample of said blood with electromagnetic radiation at a first wavelength;   illuminating said sample of blood with electromagnetic radiation at a second wavelength;   controlling the temperature of said tissue to maintain said tissue at a predetermined temperature;   collecting electromagnetic radiation reflected by said sample of blood in the tissue at the predetermined temperature and forming data signals therefrom; and   processing said data signals to calculate the blood oxygen saturation of the blood in said tissue.   
     
     
       16. The method of claim 15, wherein said controlling step comprises the steps of measuring the temperature of said tissue; controlling the temperature of said tissue by heating said tissue when said temperature of said tissue is less than said predetermined temperature.   
     
     
       17. A blood oxygen saturation monitoring system for non-invasive measurement of oxygen saturation of arterial blood in tissue of a patient, comprising: a first source of electromagnetic radiation at a first wavelength;   a second source of electromagnetic radiation at a second wavelength;   means for positioning said first and second sources of electromagnetic radiation on the patient so as to illuminate a sample of blood in the tissue;   detecting means for receiving electromagnetic radiation reflected by said sample of blood;   data processing means for calculating the blood oxygen saturation of said tissue responsive to said detected reflected electromagnetic radiation; and   means for maintaining said tissue at a predetermined temperature comprising:   a light emitting diode;   a thermal sensor having an output signal indicative of the temperature of said tissue;   a control circuit responsive to said output signal of said thermal sensor and having a feedback circuit with an adjustable setpoint; and   a core temperature probe coupled to said control circuit for monitoring the patient's body temperature and for providing a reference signal for comparison with said setpoint.   
     
     
       18. A blood oxygen saturation monitoring system for noninvasive measurement of oxygen saturation of arterial blood in tissue of a patient, comprising: a first source of electromagnetic radiation at a first wavelength;   a second source of electromagnetic radiation at a second wavelength;   means for positioning said first and second sources of electromagnetic radiation on the patient so as to illuminate a sample of blood in the tissue;   detecting means for receiving electromagnetic radiation reflected by said sample of blood;   data processing means for calculating the blood oxygen saturation of said tissue responsive to said detected reflected electromagnetic radiation; and   means for maintaining said tissue at a predetermined temperature comprising:   a light emitting diode;   a thermal sensor having an output signal indicative of the temperature of said tissue;   safety means coupled to said means for maintaining for disabling said means for maintaining thereby preventing thermal burns to said tissue in the event of a system failure, said safety means further comprising a thermal sensor failure circuit for detecting a failure in said thermal sensor and means for disabling said light emitting diode when said failure is detected.   
     
     
       19. A blood oxygen saturation monitoring system for noninvasive measurement of oxygen saturation of arterial blood in tissue of a patient, comprising: a first source of electromagnetic radiation at a first wavelength;   a second source of electromagnetic radiation at a second wavelength;   means for positioning said first and second sources of electromagnetic radiation on the patient so as to illuminate a sample of blood in the tissue;   detecting means for receiving electromagnetic radiation reflected by said sample of blood;   data processing means for calculating the blood oxygen saturation of said tissue responsive to said detected reflected electromagnetic radiation; and   means for maintaining said tissue at a predetermined temperature comprising:   a light emitting diode;   a thermal sensor having an output signal indicative of the temperature of said tissue;   safety means coupled to said means for maintaining for disabling said means for maintaining thereby preventing thermal burns to said tissue in the event of a system failure, said safety means further comprising a power sensing circuit for monitoring the power delivered to said light emitting diode and means for disabling said light emitting diode if the power delivered exceeds a predetermined value.